1. Field of the Invention
The present invention relates to a method for assaying dystrophin which is a protein defective in a human suffering from Duchenne muscular dystrophy (DMD) which is a hereditary disease.
2. Discussion of the Background
Duchenne muscular dystrophy is a hereditary disease which is developed almost only in males. A gene which is defective peculiarly to this disease is located on the X chromosome and its sequence has been elucidated [M. Konig, E. P. Hoffman, C. J. Bertelson, A. P. Monaco, C. Feenet and L. M. Kunkel: Cell, 50, 509 (1987), E. P. Hoffman, A. P. Monaco, C. C. Feeher and L. M. Kunkel, Science, 238, 347 (1987)]. If any antibody capable of specifically recognizing dystrophin which is a protein encoded by this gene is produced, a deletion or defect of dystrophin specific to this disease could be detected and such would be useful. A related method was tried by Hoffman et al., using the gene from mice suffering from a disease which is the same type as Duchenne muscular dystrophy [E. P. Hoffman, R. H. Brown, Jr. and L. M. Kunkel, Cell, 51, 919 (1987); E. P. Hoffman, C. M. Knudson, K. P. Campbell and L. M. Kunkel, Nature, 330, 754 (1987)]. However, the method of Hoffman et al. uses a gene from mice, the amino acid sequence of which is different by about 10% from that of humans, to produce the antibody so that it is inappropriate to determine dystrophin possessed by humans. Moreover, according to this method, protein having a high molecular weight such as 208 amino acid residues or 410 amino acid residues is used as an antigen and hence, the method has a shortcoming that an antibody capable of reacting not only with dystrophin but also with many other proteins is formed and that the antibody fails to specifically react with dystrophin alone. In order to compensate for the poor specificity of reaction, Hoffman et al. adopted a method using a specimen obtained by previously homogenizing cells to be tested followed by separating protein from the homogenate by electrophoresis, and then performing an antigen-antibody reaction with respect to the specimen. For this reason, the method encounters a drawback that operations are complicated and is thus unsatisfactory.
In general, conventional methods for assaying dystrophin have drawbacks in that antibodies capable of specifically reacting only with dystrophin could not be obtained since a gene from a mouse, which is different from that of a human, has been used for preparation of the antibody. Further, operations are complicated since the method comprises using a specimen obtained by previously homogenizing cells to be tested and separating protein from the homogenate by electrophoresis and performing an antigen-antibody reaction with respect to the specimen. Therefore, the present inventors have made extensive investigations to discover a method for assaying the protein in cells in a simple manner, by preparing an antiserum capable of specifically reacting only with dystrophin or an antibody fraction separated from the antiserum using a part of dystrophin encoded by human Duchenne muscular dystrophy-associated gene and performing an antigen-antibody reaction between a substance to be tested and the antiserum or antibody fraction.